This invention relates to management of power consumption and performance of a storage system. More particularly, a technology disclosed herein relates to a file system that provides data access in accordance with a policy regarding power consumption and performance.
Storage systems are becoming larger in scale as the amount of data handled by computer systems increases. Large-scale storage systems are used in data centers and the like, and their increased power consumption is posing a problem.
A technology called massive arrays of idle disks (MAID) has been proposed to deal with this problem (see U.S. Pat. No. 7,035,972). The MAID reduces the power consumption of a storage system by stopping the spinning of the disks in a disk drive that is not in use.
The MAID is applied to a storage system that is capable of power supply control (see JP 2005-157710 A). According to JP 2005-157710 A, in the case where a plurality of disk drives constitute redundant arrays of inexpensive disks (RAID), power supply is controlled separately for each management unit of a plurality of disk drives constituting the RAID.
When access to a disk drive that has stopped the spinning of its disks is requested, the access is executed after the disk drive is started up and the disks start spinning. The period of time required to start up the disk drive lowers the access performance. JP 2007-86843 A and JP 2007-164650 A disclose a technology of preventing the lowering of access performance from this cause by selecting a disk drive that is to store data based on the access frequency of the data. Specifically, the data storage location is selected such that data with a high access frequency is stored in a disk drive that is controlled to stop the spinning of its disks for a short period of time (or a disk drive that is controlled to never stop the spinning of its disks).
Another known technology of improving the access performance is to store data in a plurality of disk drives in a dispersed manner. Generally, the access performance (specifically, I/O throughput) improves more when data is dispersed among more disk drives. However, when data of one file, for example, is stored dispersedly among a plurality of disk drives, all those disk drives have to be accessed to read the file. Dispersing data in many disk drives therefore means that many disk drives need to be started up to read a single file.
JP 2007-286975 A discloses a technology of determining the placement of data in accordance with a policy regarding the above-mentioned access performance and start-up time. Specifically, in the case where improving the access performance is given priority, data is stored dispersedly in a relatively small number of disk drives, whereas data is stored dispersedly in a relatively large number of disk drives in the case where keeping the disk drive start-up time short is given priority.